The proposed work focuses on the proteasome. This enzyme complex is responsible for most cell protein degradation, including fundamental processes responsible for cell viability and function. We will ask if age-related defects in proteasome function disrupt the function of the retinal pigment epithelium (RPE), and what are the consequences of reduced proteasome function. One focus will be on defining the role of the proteasome in the RPE, where two roles are considered. Since proteasome controls processes that are essential for cell survival, a loss of proteasome function could cause RPE cell death through the accumulation of dysfunctional proteins or the disruption of critical cell pathways. Alternatively, if proteasome participates in the degradation of phagocytosed rod outer segments (ROS), decreased proteasome function could contribute to diminished processing of ROS proteins. A second focus will be to elucidate the biochemical mechanism responsible for the age-dependent loss in proteasome function. The following Aims will be pursued: (1) Define the proteolytic capabilities of the proteasome in the RPE. (a) Define the role of the proteasome in the degradation of phagocytosed rod outer segments. (b) Determine the effect of stressors on RPE proteasome function. (2) Determine age-related changes in retinal proteasome function. (a) Quantify age-related alterations in proteasome function and expression. (b) Identify post-translational modifications in proteasomal subunits. Our investigative approach will include a range of techniques in biochemistry, cell biology, immunology, molecular biology, and proteomics using rodent models of aging, transgenic mice, and cultured cells. Little information is known about proteasome function in the retina, so these studies will provide an important contribution to basic retinal physiology and the effects of aging.